The present invention relates to sulfonic acid esters of 2,4-bistrichloromethyl-6-(mono- or dihydroxyphenyl)-1,3,5-triazine and to a negative-working radiation-sensitive mixture containing these compounds in combination with a compound containing at least two acid-crosslinkable groups, and a water-insoluble polymeric binder which is soluble or at least swellable in aqueous-alkaline solutions. The invention also relates to a radiation-sensitive recording material produced therewith which is suitable for producing photoresists, electronic components, or printing plates, or for chemical milling.
The constant reduction in the size of structures, for example, in chip production, down to the range of less than 1 .mu.m requires modified lithographic techniques. In order to image fine structures, radiation is used which has a short wavelength, such as high-energy UV light, electron beams or X-rays. The radiation-sensitive mixture must be suited to the shortwave radiation. A summary of the requirements imposed on the radiation-sensitive mixture is provided in the paper by C. G. Willson entitled "Organic Resist Materials--Theory and Chemistry" [Introduction to Microlithography, Theory, Materials and Processing, edited by L. F. Thompson, C. G. Willson and M. J. Bowden, ACS Symp. Ser., 219: 87 (1983), American Chemical Society, Washington]. There is therefore an increased requirement for radiation-sensitive mixtures that can be used in the more recent technologies such as mid- and deep-UV lithography [exposure, for example, to excimer lasers at wavelengths of 305 nm (XeF), 248 nm (KrF), 193 nm (ArF)], electron beam lithography or X-ray lithography. Preferably these mixtures are also sensitive in a wide spectral range and can be used in conventional UV lithography.
Negative-working radiation-sensitive mixtures that contain bisazides as crosslinking agents and binders derived from isoprene are known. They are used as radiation-sensitive layers in the production of printing plates, printed circuits and integrated circuits. Their use in microlithography is, however, limited by various technical disadvantages. Thus, it is difficult to produce high-quality layers without defects (pinholes). The thermal stability of such mixtures is inadequate, i.e., the resist images are distorted during processing by thermal flow. Finally, their resolving power is limited to structures greater than 2 .mu.m since they exhibit undesirably high swelling even in the cured regions during the necessary development with organic solvents. This results in turn in structure distortions or inhomogeneous development processes and, consequently, in inexact reproduction of the image provided by the exposure mask.
In order to produce resist images having a resolution of better than 2 .mu.m, other negative-working radiation-sensitive mixtures have been developed which are sensitive to radiation of shorter wavelength, for example, a mixture containing a copolymer of 2,3-epoxypropyl methacrylate and 2,3-dichloropropyl methacrylate (DCOPA) or a combination of the corresponding homopolymers. However, the glass transition temperature of this mixture is too low for many applications. In particular, the mixture has an undesirably low plasma etching resistance. In addition, this resist material has to be processed with developers containing organic solvents having low environmental acceptability. Other hitherto known negative-working photoresists with an aliphatic base also exhibit a low plasma etching resistance.
EP 164 248 discloses an acid-curable mixture that can be developed in aqueous alkali, has an improved plasma etching resistance as a result of the use of aromatics and is sensitive to near-UV light (350 to 450 nm). The acid formers mentioned in this connection are, in particular, sulfonic acid ester derivatives of diazonaphthoquinone, which form weakly acidic carboxylic acids on exposure and are therefore effective only at comparatively high concentration. However, as a result of the weak absorptions and of the inadequate bleaching-out behavior of the photolytic acid former, such mixtures have a low sensitivity to deep UV radiation, electron radiation and X-rays.
U.S. Pat. No. 3,692,560 describes an acid-curable mixture containing an acid-crosslinkable melamine derivative, a novolak and chlorinated benzophenones as photolytic acid formers. These mixtures also have inadequate sensitivity in the deep-UV region. The same applies to the acid-forming derivatives of DDT which are mentioned in EP 232 972. In addition, these are highly toxic and cannot therefore realistically be used. All the same, such compounds have an appreciable sensitivity in the deep-UV region (200 to 300 nm).
Examples of compounds that form a strong acid on irradiation include, in particular, onium salts such as diazonium, phosphonium, sulfonium and iodonium salts of non-nucleophilic acids such as HSbF.sub.6, HAsF.sub.6 or HPF.sub.6 [J. V. Crivello, Polym. Eng. Sci., 23: 953 (1983)]. In addition, halogen compounds, in particular trichloromethyltriazine derivatives (EP 137 452=U.S. Pat. No. 4,619,998/4,696,888) or trichloromethyloxadiazole derivatives, o-(quinone diazide)sulfonyl chlorides, o-(quinone diazide)-4-sulfonic acid esters, bis(sulfonyl)diazomethanes, sulfonylcarbonyldiazomethanes and nitrobenzyltosylates have been recommended.
These compounds are used in negative- or positive-working radiation-sensitive mixtures. The use of such photolytic acid formers, however, entails certain disadvantages which severely restrict their possible uses in various fields of application. Thus, the onium salts have a relatively high, virtually unbleachable self-absorption in the desired wavelength region. This means that the maximum achievable resolution of the resultant radiation-sensitive mixture is limited in many cases. Furthermore, many onium salts are toxic. Their solubility in many solvents is inadequate, and for this reason only a few solvents are suitable for producing a coating solution. In addition, impurity atoms, some of which are undesirable and which may result in process interferences, particularly in microlithography, are introduced if onium salts are used, with the result that the use of such mixtures leads to unsatisfactory results. Although halogen compounds such as (quinone diazide)sulfonyl chlorides form strong hydrohalic acids, they have, in the radiation-sensitive mixture and also on certain substrates, only a limited durability. This has been improved by inserting an interlayer between substrate and radiation-sensitive layer containing compounds that form a strong acid upon exposure, but this resulted in an undesirable increase in defects and in a reduced reproducibility (DE 36 21 376=U.S. Pat. No. 4,840,867).
Although other classes of compounds that generate hydrohalic acid such as bistrichloromethyltriazine derivatives (EP 137 452) have a good acid-forming efficiency, they have an often inadequate solubility in common resist solvents. They are, in addition, frequently sweated out of the photosensitive layer under the processing conditions applied in practice, with the result that a reproducible production of the resultant layer is no longer possible.
In more recent publications by F. M. Houlihan et al., SPIE 920:67 (1988), it was shown that positive-working systems containing nitrobenzyl tosylates that form sulfonic acids with low migration tendency on exposure can be used in certain acid-labile resist formulations in addition to the above-mentioned acid formers. From these results it can be deduced that such compounds can also be used for photocurable systems. The sensitivities achieved under these circumstances and the thermal stability of the photoresist prove, however, to be inadequate.
Despite the intensive research activity hitherto carried out in this field, no radiation-sensitive mixture is known at the present time with which a negative-working radiation-sensitive recording material can be produced having a high sensitivity in the deep-UV region (200 to 300 nm), a high resolution, and an ability to be developed fully compatibly and in aqueous alkali solutions using standard lithographic processing steps.